A slight difference (7.9e-17) in calculation now exists between
the C and C# horizontal angle calculations on Windows.
This is not surprising because the atan2() function is
known to return slightly different values on other
compilers/platforms. Adjusted the tolerance for this tiny
amount of roundoff discrepancy.
It turns out different Node.js versions do math differently,
which caused a Travis CI build failure.
Scale topocentric distance the same way I scale heliocentric distance.
Adjusted diffcalc bash script and diffcalc.bat Windows batch file accordingly.
The differ now prints the final "score" so I'm less likely to make
a mistake spotting the correct maximum difference.
Removed unused variable in ctest.c DiffLine(): maxdiff.
When comparing calculations of body vectors, scale
the size of the difference by the minimum orbital
radius (or typical radius in the case of the Solar
System Barycenter).
This concludes my investigations of discrepancies between
the various language calculations. I have done as much
as I can without implementing my own trig functions,
which is not worth the effort (or the loss of efficiency
in JavaScript).
Scaling the errors relative the measurement units reveals
that the discrepancies are reasonable for the 16-digit
precision one expects from 64-bit floating point numbers.
The worst case is C vs JavaScript, with a scaled error
of about 7.2e-15. I can live with that.
A given amount of error in an angle measured in
sidereal hours is 15 times more important than the
same numeric error in an angle measured in degrees.
Scale angular errors by the range of values they
could take on. Longitude-like angles in degrees
have a range of 360, while latitude-like angles
range over 180 degrees (-90 to +90).
Split out separate Windows batch file diffcalc.bat,
just like I already split out bash script diffcalc.
